This invention relates to heat exchanger constructions, and in particular to improvements in heat exchangers embedded in concrete and asphalt to remove ice and snow from public areas, or to provide radiant heat from an interior floor, or to recover solar heat. Also the invention can be used as a heat exchanger for other purposes, such as ceiling surfaces, transport vehicles, hoppers, chutes, transport cars and other areas of industrial process.
Every year thousands of pedestrians suffer injuries when they slip and fall on ice and snow surfaces including driveways, parking lots, roadways, walkways or sidewalks made of concrete, masonry, or asphalt. Even after plowing and shoveling, a thin layer of ice usually remains to endanger those on foot and to be tracked into the building where it melts and forms slippery wet spots. The floor inside a building must be mopped dry and extra doormats provided to prevent accidents inside as well as outside the building. These injuries increase liability insurance premiums significantly, discourage customers in bad weather and thus raise the cost of doing business.
Salt is used to remove ice, but it must be applied often because it is easily washed away and it has virtually no effect upon heavy snowfall. Salt is corrosive, harming automobiles, damaging doors, fittings, trim and shopping carts. Salt also weakens the glue bond on floor tile, discolors carpets and wood molding and is an environmental hazard to many communities.
One practical solution to ice covered walkways is to warm the surface by heating the mass below. This approach can be used for space heating by warming the floor of agricultural, industrial, commercial and residential buildings. Floor heat is an explosion resistant, quiet, clean, economical, and even heat that can use a variety of fuel sources to keep floors warm and dry.
Several snowmelting/floorheating systems have been used in concrete. Electrical resistance wires have been embedded to heat the concrete to keep it warm. These wires are easy to install, but they are fragile and likely to break as the concrete settles and cracks. These breaks are difficult to locate and repair. Electric resistance systems are also very expensive to operate, because they use electricity rather than economical fuel sources like natural gas or waste heat or heat from renewable resources.
Tubes have also been embedded in concrete to convey a heated fluid which in turn conducts warmth to the surrounding concrete for the purpose of snowmelting and space heating. These tubes are made of iron or copper and more recently of polybutylene, polyethylene, or EPDM (ethylene propylene diene monomer). Metal tubes are difficult, time consuming, and expensive to install. Numerous joints are required and each joint presents a potential leak. The tubes are installed over a gravel base, and before they can be covered up, trucks and construction equipment are likely to be driven over them, deforming and displacing the tubes and weakening the joints. When metal tubing is used in concrete, leaks are often caused either by slab settling or by corrosion caused from the reaction of the concrete and metal. Metal tubes are unsatisfactory in asphalt. Metals and asphalt have significantly different co-efficients of thermal expansion and thus cycles of temperature change cause the metal to expand and the asphalt to crack.
Polypropylene and other plastic tubing have been used in concrete, although they have many important limitations. Plastic tubes allow atmospheric oxygen to enter the system resulting in severe corrosion of the pumps, boilers, and other metal parts. Rigid plastic tubes cannot withstand abuse from trucks and construction vehicles occurring between the time the tubes are laid and unprotected and the time they are covered with concrete or masonry materials. Plastic tubing and especially EPDM tubing embedded in concrete is also subject to attack from petroleum distillates, solvents, cleaning fluids and other agressive chemicals that seep through cracks which develop in the concrete as it ages. Polybutylene, polypropylene and polyethylene plastic tubes are subject to complete failure at temperatures exceeding 220.degree. F. when control systems or boilers allow fluid temperatures to exceed that temperature for a certain period (a condition known as "boiler runaway"). The entire system may be irreparably damaged.
Metal and some plastic tubing are subject to severe damage when the fluid inside is accidentally allowed to freeze. Water frozen in rigid metal or some plastic tubes can damage the floor and cause water damage to the building and furnishings.
Plastic tubing is unsatisfactory in asphalt. Asphalt is applied at about 275.degree.-350.degree. F. and is then rolled and compacted. Plastic tubing is incapable of withstanding the elevated temperatures and pressures of asphalt application.
Thus, while there are some techniques for melting snow and ice from the surface of concrete slabs, there has been no acceptable way to melt snow and ice from the surface of asphalt. Prior art includes the use of hose to conduct fluids, but applicants have invented an improved hose construction that is designed to emit radiation as well as conduct fluids. Hose is generally designed as and thought to be an insulated conduit; but the new construction is designed to efficiently release heat to air, water or solid environments. In contrast to prior art metal pipe, plastic pipe, hose or elastomeric extrusions, applicants' improved hose construction works in concrete or asphalt, is easier and less expensive to install, is immune to most oils and cleaning agents, resists invasion from corrosion-causing atmospheric oxygen, works at higher fluid temperatures, is not damaged by freezing fluids within, is crush and abrasion resistant, has no joints under floor, is more reliable, and lasts longer. The construction makes automatic ice and snow melting available for the first time in the millions of square feet of asphalt laid each year.